i got this truck on the road a month or so ago. she is getting all the bugs worked out. well she has 4" lift and 35" tires on 1 ton truck. 350 4 speed. bla bla bla. so when we get to 55-up she starts to vibrate bad. and faster makes it worse. so i figure tires need good balence job. add to list to fix. then when i brake it shakes like crazy the faster i am going the worse it gets. so i figure the rear 13"x 3.5" dually drums are shot as thay sure looked it to me. so add this to the list to fix. i had checked it over before going on the road again after she was parked for over 4 years in a farmers headge row. short story is she got a makeover more than chip fosse or pimp my ride boys would have even looked at 1 time and just said sorry hell no. but i fixed it up as i found all the stuff cheep. so the vibration was getting to me. so i pulled the drive shaft today. just to make sure the joints were good. and 1 was a tiny bit tight. and the slip for the shaft was getting some play. but the carrier bearing for the 2 peice shaft was funky. the rubber isolator that holds it was realy loose and had 1/4" play to the top of the shell. i think at speed under load it was letting the shaft hop up and down out of balence alot. so i had a spare 1 ton shaft same length and it was a 1 peice shaft also. great no more 2 peice shaft anymore. so i installed it in the truck. then i went out for a test drive. and W.O.W what a big diffrence in the truck even from a start off. 95% of my problems are gone and i just need to balence the tires at work and she will be great. the big break shake is no more at all. so if you are having fun trying to pinpoint a bad vibe or shake at speed . dont rule out the shaft or shafts in your driveline.